Carburetor



July 11, 1961 I 2,991,985

CARBURETOR Filed Sept. 4, 1958 IN VENTO R.

United States Patent Ofifice 2,991,985 Patented July 11, 1961 2,991,985 CARBURETOR Stanley H. Mick, St. Clair Shores, Mich., assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Sept. 4, 1958, Ser. No. 758,995 7 Claims. (Cl. 261-41) The present invention relates to a system which can be applied to carburetors for use with internal combustion engines for improving mass air flow metering. By mass air fiowmetering it is meant that a pressure force proportional to the square of mass rair flow is created by passing the air through a venturi and this force suitably applied to a fuel orifice to obtain the requisite fuel flow.

Present carburetors normally operate on two systems: (a) the idle system using manifold vacuum to draw fuel through'the metering orifice, and (b) the high speed system operating on the mass air flow principle. However, using two separate systems causes problems in obtaining uniformv flow in the range where the second system starts or stops flowing. In addition, the idle system requires extensive tailoring to determine the size and position required for the fine holes which are normally progressively subjected to manifold vacuum as the throttle is opened from its idle setting.

In the subject invention, the carburetor would meter fuel on the mass air flow principle at all operating conditions. In the past, this has been prevented mainly because aventuri generated vacuum force or signal is not sufficient at idle and low, air flows to lift the fuel head from the bowl level to the highest point in the fuel passages. This head is normally established to prevent the fuel bowl from draininginto the engine when the vehicle is parked on various slopes. The proposed carburetor eliminates the requirement that the metering signal lift the fuel during low air flow conditions by providing a fuel transfer passage which takes the metered fuel at the bowl level and lifts-it the required head then transfers the fuel and discharges it below the throttles into the manifold. In the present system it is proposed that manifold vacuum be used to provide the pressure differential to transfer this fuel.

In the present invention a fuel metering venturi is disposed in the carburetor induction passage and is combined with a fuel metering orifice in such a way that under all operating conditions the air flow through the venturi will determine the quantity of fuel flow through the metering orifice. In the present device a transfer passage is formed within the main fuel metering passage and is provided with a small orifice terminating posteriorly of the main fuel metering orifice. The transfer passage communicates at its other end with the induction passage posteriorly of the throttle valve. Thus, manifold vacuum at all times acts on the transfer passage and under low air flow conditions when the metering signal is too weak to overcome the aforenoted head and to cause the flow of fuel in the normal manner, manifold vacuum will pick up the metered fuel and transfer the same through the transfer passage to discharge the same posteriorly of the throttle. By suitably proportioning the transfer passage orifice in relation to the main fuel metering passage, more specifically making the former relatively small, manifold vacuum will have no effect on fuel metering but rather will only provide the motivating force whereby previously metered fuel is caused to flow under low air flow conditions. when the venturi signal would be otherwise too weak to achieve such flow.

An additional feature of the present invention includes the mounting of the metering orifice as well as the transfer passage orifice in a floating member whereby the orifices are always maintained in a constant relationship to the fuel level in the float bowl chamber. In this way changes in the fuel head within the float bowl will be prevented from having any effect on the metering action of the venturi signal.

Other objects and advantages of the present invention will be apparent from a perusal of the detailed description which follows.

The drawing is a schematic representation of a carburetor embodying the subject mass air flow metering system.

For illustrative purposes the present invention has been shown on a carburetor indicated generally at 10. Carburetor 10 includes an air induction passage 12 having a throttle and choke valves 14 and 16 rotatably mounted therein. ,In the particular carburetor shown, a plurality of casings are utilized with the throttle valve being mounted in a throttle body 18, a float bowl casing 2%) which also includes a venturi section 22 of induction passage 12 and a casing 24 housing choke valve 16 and providing the cover for float bowl chamber 26.

Fuelis supplied to float bowl chamber 26 through a conventional type float controlled fuel inlet valve device indicated generally at 28. In order to simplify the present invention and since the float controlled inlet valve device 28j constitutes no part of the present invention, the latter has been schematically repreesnted. In general, the fuel inlet valve itself is disposed at 30 and is controlled by a float member 32 suitably articulated thereto through a conventional linkage arrangement.

The present invention is illustrated on a mass air flow type carburetor in which it is desired to meter the fuel under all conditions in accordance with mass air flow. Accordingly, a booster or metering venturi 34 is disposed in induction passage 12 and is disposed concentrically of the main venturi section 22. Metering venturi 34 is in general of frusto-conical cross section and is supported upon a strut member 36 which extends across the venturi mouth and has a passage 38 formed therein. Passage 38 terminates in a depending portion 40 in'communication with the venturi throat 42.

Passage 38 continues from strut 36 into casing 20 extending transversely thereof and terminating in a conduit member 44. Member 44 in turn includes a downwardly extending section 46 which terminates at its lower end in a metering orifice 48 disposed below the fuel level within float chamber 26.

As air flows through induction passage 12 and venturi 34, a pressure differential due to the atmospheric pressure in chamber 26 and the mass air flow induced vacuum at end 40 of passage 38 will cause fuel to flow through metering orifice 48 and to be discharged into venturi 34, Fuel will flow in this manner during high air flow conditions when the metering vacuum force is of a sufficiently high magnitude to lift the fuel column from the fuel level in chamber 26 to passage 38 and discharge the same into induction passage 12.

In order not to restrict the flow of air through the induction passage under high air flow conditions, venturis 22 and 34 must be relatively large. As a consequence, under low air flow conditions, particularly as would occur during engine idling, the fuel metering vacuum force generated within venturi 34 is relatively low and inadequate to 'cause fuel to flow through passage 38. As already noted, it is the object of the present invention to provide a fuel metering system whereby the fuel is metered in accordance with mass air flow under all operating conditions. Accordingly, means is provided whereby the fuel may be lifted by a non-metering force to overcome the predetermined fuel head under conditions when the metering signal is inadequate to effectuate such flow.

To this end, a fuel transfer passage 50 is formed in the float bowl casing 20. Passage 50 communicates at one end with a generally horizontally extending conduit 52 which terminates in a downwardly depending section 54 concentrically disposed within section 46 of the main fuel metering conduit 44-. Section 54 of conduit 52 terminates in a relatively small orifice 56 spaced posteriorly in relation to fuel flow of main fuel metering orifice 48. Orifice 56 is located at the level of fuel in float bowl 26. Fuel transfer pasasge 50 also extends through throttle body 18 and communicates with a tube 58 extending within induction passage 12 posteriorly of throttle valve 14.

If the same fuel-air ratio was adequate to maintain engine operation during idling as during normal running, the venturi vacuum signal would provide the requisite fuel flow. However, since engine efliciency is low during idling, it is necessary to provide means for enriching the fuel-air ratio under this operating condition. Accordingly, a passage 60 is provided in casings 18 and 20 and communicates at one end with the main fuel metering passage 38 and terminates at its other end in an orifice 62 open to induction passage 12 posteriorly of throttle valve 14. In this way manifold vacuum reinforces the venturi vacuum signal in passage 38 to increase fuel flow during idling operation.

Orifice 56 is made relatively small so that manifold vacuum will have a negligible effect on the quantity of fuel drawn through the metering orifice 48 during normal engine operation. Thus manifold vacuum is utilized under normal engine operation to provide the force necessary to effectuate fuel flow the quantity of which is metered by the vacuum force generated in venturi 34. During idling operation, however, manifold vacuum also reinforces the metering signal to increase the fuel-air ratio.

In making the transition from high air flow conditions to low air flow conditions, which accompanies a closing of throttle valve [14, fuel will first be discharged into the induction passage first through passages 3840 within venturi 34 followed by discharge through the fuel transfer passage 50 as air flow is diminished.

As already noted, and in order to avoid excessive restriction to air flow at high speeds, ventun's 22 and 34 are made relatively large. This, however, results in an extremely small metering signal during low air flow conditions, such as when idling. For illustrative purposes, the low air flow vacuum signal may be less than a tenth of an inch of the fuel head. This, of course, makes the fuel metering very sensitive to the level of fuel in float bowl chamber 26 under idling conditions. In other words, and to continue the illustration, if the fuel level lowers a tenth of an inch, relative to the fuel metering orifice and the fuel transfer passage orifice, the engine will starve because it is too lean, and if on the other hand the level raises a tenth of an inch, the engine will stall because it was too rich. Thus to avoid stalling caused by fuel level changes, it is highly desirable that the main fuel metering jet 48 and the transfer passage orifice 56 follow the level of fuel in chamber 26.

Proper orientation of the orifices 48 and S6 is achieved by disposing these orifices in a float member indicated generally at 64. Conduit sections Y46 and 54 are respectively fixedly disposed within float 64 and connected to passages 44 and 52 through flexible sleeves 66and 68. In this way as the fuel level in float chamber 26 varies even slightly, float 64 will follow the level changes and accordingly maintain orifices 4-8 and 56 in a constant relationship to the fuel level thereby insuring proper metering of the fuel under all conditions.

Flexible sleeves 66 and 68 may be formed of any suitable material, such as synthetic rubber or plastic, which will not suffer any deleterious effects by exposure to gasoline.

An adjustable idle mixture control needle valve 70 is mounted in throttle body 18 and terminates in a tapered section 72 adapted to coact withorifice 62 to adjust the quantity of said fuel flow in the normal manner.

While the concept of providing a fuel transfering force to facilitate fuel flow under conditions when a metering force is relatively weak has been shown as applied to a mass air flow type fuel system, it is also within the scope of this invention to apply this principle to other types of fuel metering devices. To illustrate briefly, this same system can be applied to a variable throat carburetor. In the variable throat carburetor the fuel is normally discharged into relatively slow moving air at low air flows and has a chance to collect before passing the throttle blade. In this case if the transfer passage is provided to pick up the fuel at the metering point and discharge it into the manifold past the throttle, the fuel flow to the engine will be more uniform and would respond more rapidly to small changes in metering fuel rate.

It is obvious that various structural modifications might be made in the schematic representation of the subject invention within the teaching of the invention as set forth in the above description as well as the drawing.

I claim:

1. A charge forming device for an internal combustion engine comprising an induction passage, a throttle valve rotatably disposed within said passage, venturi means disposed in said induction passage anteriorly of the throttle valve, a main fuel passage disposed Within said venturi means and terminating in an end disposed within the throat of the venturi means so as to subject said passage to a vacuum force proportional to the square of the mass ofair flow therethrough, a fuel chamber, the other end of said main fuel passage terminating in a metering orifice disposed below the level of the fuel in said chamber, and a fuel transfer passage terminating at one end in communication with the induction passage posteriorly of the throttle valve, the other end of the fuel transfer passage terminating in an orifice disposed within the main fuel metering passage posteriorly of the main fuel metering orifice, said main fuel passage including a section interconnecting the end disposed within the venturi means and said other end, said section being spaced vertically above the fuel transfer passage whereby air flow through the venturi will control the quantity of fuel flow through the main fuel passage.

2. A charge forming device for an internal combustion engine comprising an induction passage, a throttle valve rotatably disposed within said passage, venturi means disposed in said induction passage anteriorly of the throttle valve, a main fuel passage disposed within said venturi means and terminating in an end disposed within the throat of the venturi means so as to subject said passage to a vacuum: force proportional to the square of the mass of air flow therethrough, a fuel chamber, the other end of said main fuel passage terminating in a metering orifice disposed below the level of the fuel in said chamber, and a fuel transfer passage terminating at one end in communication with the induction passage posteriorly of the throttle valve, the other end of the fuel transfer passage terminating in an orifice disposed within the main fuel metering passage posteriorly of the main fuel metering orifice and substantially at the level of the fuel in said chamber, said main fuel passage including a section interconnecting the end disposed within the venturi means and said other end, said section being spaced vertically above the fuel transfer passage whereby air flow through the venturi will control the quantity of fuel flow through the main fuel passage.

3. A charge forming device for an internal combustion engine comprising an induction passage, a throttle valve rotatably disposed within said passage, venturi means disposed in said induction passage anteriorly of the throtfle valve, a main fuel passage means disposed Within said venturi means and terminating in an end disposed within the throat of the venturi means so as to subject said passage to a vacuum force proportional to the square of the mass of, air flow therethrough, a fuel chambenthe other end of said main fuel passage means. terminating in a metering orifice disposed below the level of the fuel in the float bowl chamber, a fuel transfer passage means terminating at one end in communication with the induction passage posteriorly of the throttle valve, the other end of the fuel transfer passage means terminating in an orifice disposed within the main fuel metering passage posteriorly of the main fuel metering orifice and float means associated with said main fuel passage means and said transfer passage to maintain orifices in a substantially constant relation to fuel level in said chamber.

4. A charge forming device as set forth in claim 3 in which the main and transfer fuel passage means respectively include sections containing the associated orifices, and flexible conduit means connecting each section to its respective passage means.

5. A charge forming device as set forth in claim 4 in which the fuel transfer passage section is disposed within the main fuel passage section in concentric relation therewith, said sections coacting to define an annular fuel passage therebetween.

6. A charge forming device for an internal combustion engine comprising an induction passage, a throttle valve disposed in said induction passage, venturi means disposed in said induction passage anteriorly of the throttle valve, a fuel chamber, a main fuel metering passage terminating at one end in said venturi means so as to be exposed to .a fuel metering force proportional to a square of the mass air flow through the venturi means, the other end of said fuel passage terminating in a main fuel metering orifice disposed below the level of fuel in said chamber, a bypass fuel passage communicating at one end with said main fuel passage intermediate the fuel metering orifice and the venturi means, said bypass passage terminating at its other end in an orifice open to the induction passage posteriorly of the throttle valve, a fuel transfer passage communicating at one end with said induction passage posteriorly of the throttle valve, the other end of the fuel transfer passage including a section disposed within said m'ain fuel metering passage, said section terminating in an on'fice spaced from said main fuel orifice and located substantially at the level of the fuel within the fuel chamber.

7. A charge forming device for an internal combustion engine comprising an induction passage, a throttle valve disposed in said induction passage, venturi means disposed in said induction passage anteriorly of the throttle valve, a fuel chamber, a main fuel metering passage terminating at one end in said venturi means so as to be exposed to a fuel metering force proportional to a square of the mass air flow through the venturi means, the other end of said fuel passage terminating in a main fuel metering orifice disposed below the level of fuel in said chamher, an idle signal boost passage communicating at one end with said main fuel passage intermediate the fuel metering orifice and the venturi means, said boost passage terminating at its other end in an orifice open to the induction passage posteriorly of the throttle valve, a fuel transfer passage communicating at one end with said induction passage posteriorly of the throttle valve, the other end of the fuel transfer passage including a section disposed within said main fuel meter-ing passage, said section terminating in an orifice spaced from said main fuel orifice and located substantially at the level of the fuel within the fuel chamber and means for maintaining the main fuel passage and fuel transfer passage orifices at a substantially constant level relative to the fuel level in said chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,621,030 Henning Dec. 9, 1952 2,752,136 Gardner June 26, 1956 2,766,974 McConnell Oct. 16, 1956 2,771,282 Olson et al. Nov. 20, 1956 2,807,449 Manning Sept. 24, 1957 

